Calcium hypochlorite blended tablets

ABSTRACT

A non-Division 5.1 Oxidizer tablet consisting essentially of a blend of hydrated calcium hypochlorite with magnesium sulfate heptahydrate, wherein the blend contains at least about 17% by weight of water based on the total weight of the blend and the dissolving rate of the tablet is less than 150 grams per day.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to tablets having diminished fireproducing properties and is a slow dissolving product containingselected mixtures of hydrated calcium hypochlorite with magnesiumsulfate heptahydrate.

2. Brief Description of Art

Hydrated calcium hypochlorite is a strong oxidizer and as such can causea severe increase in the burning rate of combustible material with whichit comes in contact. This oxidation characteristic can cause problemsboth in the transport and storage of the product. For example, firesinvolving calcium hypochlorite can be quite vigorous, particularly whencombustible material is present, including the product's packagingmaterial itself (e.g., plastic, cardboard). The blends of hydratedcalcium hypochlorite and magnesium sulfate heptahydrate of the inventionare not classified as a “Division 5.1 Oxidizer” (i.e. they do notincrease the burning rate of combustible material) as measured by aninternationally recognized test standard, i.e., the United NationsProtocol: Transport of Dangerous Goods: Manual of Tests and Criteria,Section 34; Classification Procedures, Test Methods, and Criteriarelating to Oxidizing Substances of Division 5.1.

Products that are “Division 5.1 Oxidizers” are by definition “dangerousgoods” for purposes of transport. The following references havediscussed this fire-causing problem and offered solutions to it.

U.S. Pat. No. 3,793,216 (Feb. 19, 1974) (assigned to Pennwalt) teachesadding water in the form of a hydrated inorganic salt to anhydrouscalcium hypochlorite (less than 1% water) so that the total resultingwater in the blend was from 3 to 13% resulting in a product that“provides resistance to exothermic, self-propagating decomposition whencontacted by flame, spark, or a contaminating organic substance”. Thetest used in this patent to verify this property was an “ignition test”,which contacts the test sample (from 10 to 500 grams) with a lit match,or a drop of glycerin or 2-propanol. Ignition and self-propagation ofburning are indicators of failure. Blends that have a delayed reaction,a less vigorous reaction, or a localized reaction compared to anhydrouscalcium hypochlorite were considered to be successful blends. However,this “ignition test” is not a demanding test. Since no fuel is presentthe procedure does not test the oxidizing properties, i.e., they couldstill increase the burning rate of combustible materials. In fact, aswill be shown below, many blend products described by this Pennwaltpatent pass this ignition test but would still be classified as“Division 5.1 Oxidizers”.

U.S. Pat. No. 4,201,756 (May 6, 1980), (assigned to Olin) teaches thecoating of calcium hypochlorite with a plurality of layers of inorganicsalts. The first layer must be comprised of salts of Periodic TableGroup I alkali metal salts (sodium, potassium, lithium, rubidium, cesiumor francium.) The salt must be a chloride, chlorate, nitrate, bromide,bromate, or sulfate. The first layer forms a barrier so thatincompatible salts such as basic aluminum sulfate, alkalized magnesiumsulfate, and sodium borates may be coated with a second layer on thepre-coated calcium hypochlorite without physical contact with thecalcium hypochlorite. See column 17, lines 36 to 54. The layers of saltform a physical barrier, which resists dusting and degradation duringhandling, and also decreases propensity for ignition and self-sustaineddecomposition when contacted by a lighted match or incompatible organicmaterials.

There are many differences between this Olin patent and the presentinvention. First, the requirement that an inert alkaline salt (such assodium chloride) be added as a barrier between calcium hypochlorite anda material such as magnesium sulfate heptahydrate is not necessary.Second, the requirement that the final water content of the coatedcalcium hypochlorite be between 0.5 and 10% is actuallycounter-productive for reducing the oxidizing behavior of calciumhypochlorite. As such, the mechanism is different from that disclosed inthis invention, which involves physically mixing the two substances sothat they are in physical contact with each other, and maintaining awater content of at least 17%.

The best indicator of the difference between the two ideas is shownusing Example XIV in the Olin patent. The example shows that calciumhypochlorite encapsulated with sodium chloride (approximately 21% byweight) prevented ignition of the material when contacted with a lightedmatch, i.e., it failed to undergo self-sustained decomposition. Ourexperiments show that physically blending 21% sodium chloride withcalcium hypochlorite actually accelerates burning. As stated above, themechanism is therefore different.

In addition, calcium hypochlorite tablets have demonstrated very fastdissolving rates in water. For example, as shown in U.S. Pat. Nos.4,876,003 and 4,928,813 (both issued to Casburg and were assigned toOlin), plastic sleeves were positioned around the tablet to slow downthe dissolving rate of calcium hypochlorite tablets. When placed aroundthe tablets, the tablets last longer, thus providing convenience inchlorinating swimming pools and other applications. However, suchplastic sleeves after use, must be removed from the skimmers, feedersand floaters for the swimming pools where they were used. This removaland discarding can be inconvenient to the pool owner. Alternatively,finely divided polyfluorinated polymer has been added to calciumhypochlorite tablets to cause the tablets to dissolve slower. See U.S.Pat. Nos. 4,970,020 and 5,205,961. Other chemical blends for makingcalcium hypochlorite tables are disclosed in U.S. Pat. Nos. 4,145,306;4,192,763; 4,692,335; 4,865,760; 4,961,872; 5,009,806; 5,164,109; and5,753,602.

There is still a need in this art to produce blended calciumhypochlorite tabletted products that are (1) relatively slow dissolvingproduct that does not require the use of a plastic sleeve or insolublematerial and (2) is not classified as a Division 5.1 Oxidizer and whichhas enhanced safety. (i.e., diminished fire-producing properties). Thepresent invention provides a solution to that need.

BRIEF SUMMARY OF THE INVENTION

Therefore, one aspect of the present invention is directed to anon-Division 5.1 Oxidizer tablet consisting essentially of a blend ofhydrated calcium hypochlorite and magnesium sulfate heptahydrate,wherein the water content of the blend is at least about 17% by weightof the blend and the average dissolving rate of the tablet is less than150 grams per day.

The tablet of the present invention is not a Division 5.1 Oxidizer andwill produce fires of dramatically diminished intensity compared to theabove-noted prior art calcium hypochlorite-containing blends. Becausethe products of the present invention are not classified as Division 5.1Oxidizers, they are not considered dangerous goods for purposes oftransport and thus their transportation costs are lower than theabove-noted prior art blends.

Also due to the dramatically reduced intensity of any fire involvingthese tablets (compared to currently marketed calcium hypochloritedihydrate tabletted products) the public good is served by the greatlyenhanced safety in the storage and transportation of the product.

DETAILED DESCRIPTION OF THE INVENTION

The term “non-Division 5.1 Oxidizer composition” as used in the presentspecification and claims refers to any blend of calcium hypochloritehydrate and magnesium sulfate heptahydrate that is not classified as aUN Division 5.1 Oxidizer according to standard testing procedures now ineffect.

The term “tablet” is used in the present specification and claims tocover any shape or size tablet, or other compressed shaped product madeof a blend of the two critical materials. Such tablets do not coverloose granular materials such as covered by copending U.S. patentapplication Ser. No. 10/271,375 filed on Oct. 15, 2002. Such tablets maybe made according to any conventional tablet-making process and/or anyconventional equipment that is used for making pool sanitizer tablets.

The term “blend” is used in the present specification and claims referto any homogeneous or near homogeneous mixture of the two criticalmaterials. It does not include encapsulated or layered products such ascovered in U.S. Pat. No. 4,201,756.

The term “hydrated” as used in conjunction with calcium hypochloriteproducts in the present specification and claims refers to any calciumhypochlorite product that has a water content of at least 5% by weightof calcium hypochlorite product. Preferably, the compositions of thepresent invention consist of commercial “hydrated” (5.5% to 16% water)calcium hypochlorite, CAS number [7778-54-3] and magnesium sulfateheptahydrate, CAS number [10034-99-8]. These preferred blends do notaccelerate burning and are therefore non-oxidizers (as measured by theindustry standard oxidizer classification test, i.e., United NationsProtocol Transport of Dangerous Goods—Oxidizing Substances of Division5.1).

The term “average dissolving rate” as used in the present invention,unless otherwise identified, is used to mean the static averagedissolving rate of the tabletted blends of the present invention in astanding volume of water.

As stated above, the tablets of the present invention have an averagedissolving rate of less than about 150 grams/day. In other words, a 300gram tablet will take at least 2 days to dissolve completely in astanding (non-flowing) body of water. Preferably, the average dissolvingrate is less than 100 grams per day for the tablets of the presentinvention. It should be recognized that the average dissolving rate ofthe tabletted blends of the present invention will generally have higherdissolving rates in flowing water conditions such as in a skimmer or afeeder in a swimming pool.

The composition preferably contains at least about 25% by weight ofmagnesium sulfate heptahydrate and less than about 75% by weight ofhydrated calcium hypochlorite. More preferably, these compositionscontain from about 25% to about 40% magnesium sulfate heptahydrate andabout 60% to about 75% by weight of hydrated calcium hypochlorite.

Also, the amount of water in the blend should be at least about 17% byweight of the total blend; more preferably, about 18% to about 24% byweight of the blend. The granular magnesium sulfate heptahydrate isphysically blended with granular calcium hypochlorite to produce anessentially homogeneous granular mixture. As stated above, the blendsare not classified as UN Division 5.1 oxidizers.

The tabletted composition of the present invention may also containsmall amounts of other materials as long as the presence of thosematerials does not cause the resulting product to be classified as aDivision 5.1 Oxidizer.

One preferred material is lime (Ca(OH)₂) which may be included inamounts up to about 3% by weight; more preferably, from 0.1% to about 2%by weight of the total blend of the two critical ingredients.

The amount of water in the tabletted product may be calculated by anystandard analytical method for measuring water in chemical products likethese. Our preferred method is thermogravimetric analysis (TGA).

The tabletted products of the present invention may be made fromgranular blends of the two critical ingredients (with or withoutoptional additives such as lime) according to any conventionaltabletting process and equipment normally used for making calciumhypochlorite hydrate-containing tablets. Any suitable equipment thatproduces molded compacted products such as tablets, caplets orbriquettes, or other known molded compacted products, using the blendsof the present invention may be used. Any shape or size tablet may beused. One preferred form of tablet is shown in U.S. Pat. No. 4,876,003.The preferred size tablet of that cylindrical shape is about 4 inches inlength and about 1 inch in diameter. Preferred tabletting equipmentincludes hydraulic presses (such as Hydratron or Bipel hydraulic press).Any suitable dwell times and pressures may be used in operating suchhydraulic presses. Specifically, these tablets are useful as watertreatment sanitizers (e.g. in swimming pools and spas), and areespecially safer to transport and store than calcium hypochloriteitself.

While not a preferred embodiment, it may be useful for some applicationsto place a plastic sleeve over the tabletted blends of the presentinvention to obtain a tabletted product that has even longer dissolvingtimes.

The present invention is further described in detail by means of thefollowing Examples and Comparisons. All parts and percentages are byweight and all temperatures are degrees Celsius unless explicitly statedotherwise.

EXAMPLES

The test for oxidizing substances described in Section 34 of the UnitedNations Protocol was used to determine the characteristics of thevarious blends listed in the table below. This test is much moredemanding than the glycerin “ignition” test (described earlier),requiring the presence of a substantial amount, i.e., up to 50% byweight, of a fuel (cellulose) rather than one drop of potential fuel.The detailed test method is described in the United NationsRecommendations on the Transport of Dangerous Goods; Manual of Tests andCriteria; Third Revised Edition; Section 34 “Classification Procedures,Test Methods and Criteria Relating to Oxidizing Substances of Division5.1. In the test, the relative burning rates of the various calciumhypochlorite products are compared to those of other known oxidizers. Onthe basis of this test, a product can be defined as an oxidizer or anon-oxidizer. The test method states that “This test method is designedto measure the potential for a solid substance to increase the burningrate or burning intensity of a combustible substance when the two arethoroughly mixed. Tests are conducted on the substance to be evaluatedmixed with dry fibrous cellulose in mixing ratios of 1:1 and 4:1, bymass, of sample to cellulose. The burning characteristics of themixtures are compared with the standard 3:7 mixture, by mass, ofpotassium bromate to cellulose. If the burning time is equal to or lessthan this standard mixture, the burning times should be compared withthose from packing group I or II reference standards, 3:2 and 2:3, bymass of potassium bromate to cellulose respectively.”

By definition, a substance that is not Division 5.1 Oxidizer (i.e., notan oxidizing substance) is any substance which, in both the 4:1 and 1:1sample-to-cellulose ratio (by mass) tested, does not ignite and burn, orexhibits mean burning times greater than that of a 3:7 mixture (by mass)of potassium bromate and cellulose.

The following blends of both hydrated and anhydrous calcium hypochloritewith other materials were evaluated using the test method discussedabove.

TABLE 1 Testing results of various calcium hypochlorite (anhydrous andhydrated) blends using the UN Division 5.1 oxidizer classification test.% H₂O in 5.1 Example Blend Components Ratio blend Oxidizer Blends with“anhydrous” Ca(OCl)₂ 1 Ca(OCl)₂/CaSO₄.2H₂O 80/20 5.0 Yes 2Ca(OCl)₂/Na₂B₄O₇.5H₂O 80/20 7.0 Yes 3 Ca(OCl)₂/Na₃PO₄.12H₂O 85/15 9.5Yes 4 Ca(OCl)₂/MgSO₄.7H₂O 90/10 6.0 Yes 5 Ca(OCl)₂/MgSO₄.7H₂O 75/25 13.5Yes 6 Ca(OCl)₂/MgSO₄.7H₂O 70/30 16.0 Yes Blends with “hydrated” Ca(OCl)₂7 Ca(OCl)₂.2H₂O/CaSO₄.2H₂O 80/20 9.0 Yes 8 Ca(OCl)₂.2H₂O/Na₂B₄O₇.5H₂O80/20 11.0 Yes 9 Ca(OCl)₂.2H₂O/Na₃PO₄.12H₂O 85/15 13.8 Yes 10Ca(OCl)₂.2H₂O/MgSO₄.7H₂O 90/10 10.5 Yes 11 Ca(OCl)₂.2H₂O/MgSO₄.7H₂O75/25 17.3 No 12 Ca(OCl)₂.2H₂O/MgSO₄.7H₂O 70/30 20.5 No

Note that the tests were run both with anhydrous (less than 1% water)and hydrated (6% water) calcium hypochlorite, although it should benoted that hydrated calcium hypochlorite did not exist on a commercialbasis when the earlier Pennwalt work was done.

The tests show that the first four blends in the table (Examples 1–4),while they are within the scope of the Pennwalt patent, do not pass theUN Division 5.1 Oxidizer test. All are classified as oxidizers by thattest.

The only blends that pass the UN Division 5.1 Oxidizer (i.e., are notoxidizers) are the 75/25 and 70/30 hydrated cal hypo/MgSO₄.7H₂O blends(Examples 11 and 12). Note that neither the 75/25 nor the 70/30anhydrous calcium hypochlorite/MgSO₄.7H₂O blends (Examples 5 and 6) passthe UN Division 5.1 Oxidizer test. Both the 75/25 and 70/30 hydrated calhypo/MgSO₄.7H₂O blends are outside of the scope of the Pennwalt patentfor at least two reasons. First, as stated earlier, hydrated calciumhypochlorite did not exist commercially at that time, and, second, theproducts both contain substantially more than 13% water cited in thePennwalt patent.

Further testing also showed that the 70/30 blend of hydrated calciumhypochlorite and magnesium sulfate heptahydrate did not accelerate theburning of the product in 5-lb. plastic bottles. The bottles containingthe blends of Examples 11 and 12, when artificially set on fire usingkerosene and a torch burned slowly, showing a burn rate similar to theempty plastic packages themselves. Conversely, calcium hypochloritehydrate alone in the same quantity and packaging, burned quitevigorously.

Continuous Flow Tabletting Dissolving Test

Six formulations noted below in Table 2 were prepared by firsthomogenously blending the listed ingredients together for eachformulation and then preparing six batches of tablets of such blendsthat weighed 285 grams each. These tablets were produced on either Bipelor Hydratron hydraulic tabletting machine into a shape similar to thecylindrical tablets shown in U.S. Pat. No. 4,876,003 (Casberg et al.).The Bipel press was a 3-tablet, 70 ton Split Preformer Bipel HydraulicPress. The batches made with it had dwell times between 2.4 and 3.0seconds and the pressures were 2800–3100 psig. The Hydratron Press was a30 ton, Single Tablet, Hydratron Hydraulic Press. The batches made withit were run at 0.6 second dwell and a pressure of 2100–2200 psig.

TABLE 2 Calcium Hypochlorite Hydrate/Magnesium Sulfate Heptahydrate/LimeFormulations Formulation Ca(OCl)₂.2H₂0 MgSO₄.7H₂0 Ca(OH)₂ 1 70 30 0 2 3027 3 3 70 28.5 1.5 4 70 29 1 C-5 98.5 0 1.5  C-6* 98.5 0 1.5*Formulation had a plastic sleeve around the tablet as shown in U.S.Pat. No. 4,876,003.

These tablets of such formulation were then placed in separate skimmersin a swimming pool. The flow rate of water through the skimmers was 30gallons per minute. The size basket of the skimmer was 6.5 inches. Thetest was run with the water flow on for 12 continuous hours and then offfor 12 continuous hours for each day. During the off period, the tabletswere submerged under water in the skimmer. These tablets were removedfrom the skimmers at periodic time intervals and weighed. Theapproximate average dissolving rates of each formulation over a 2 to6-day test period are shown below in Table 3.

TABLE 3 Average Dissolving Formulation Rates (grams/day) 1 137 2 73 3 944 73 5 790 6 118

Static Dissolving Tests

Four formulations noted below in Table 4 were prepared by firsthomogenously blending the listed ingredients together for eachformulation and then preparing tablets of such blends. Each tabletweighed 285 grams. These tablets were produced on a hydraulic tablettingmachine all from batches about 200 pounds each into a shape similar tothe cylindrical tablets shown in U.S. Pat. No 4,876,003 (Casberg etal.). These tablets were all produced on the 30 ton, Single Tablet,Hydratron Hydraulic Press. The pressing pressure for all batches was2500 to 2800 psig with a 0.2 second dwell.

TABLE 4 Formulation Ca(OCl)₂.2H₂0 MgSO₄.7H₂0 Ca(OH)₂ 1 98.5% — 1.5% 2  70%   30% — 3   70% 28.5% 1.5% 4   70%   27%   3%

Each pre-weighted tablet was placed in a basket in 3 liters of water.There was no stirring of the water for 5½ hours. The tablet was removedand re-weighed, then the water was mixed vigorously for 30 minutesbefore being analyzed for Cl₂ content. The water was allowed to settleand the tablets were placed back in their baskets until next time formeasurement. The mixing and analyzing procedures were repeated. Theresults of these measurements are shown in Table 5 below.

TABLE 5 g C12 Dosage into pool Dosage per Weight % AvC12 in solution perCapsule, (?) Capsule (?) per Formulation Time Hours Weight g. Loss Temp.° C. in solution (by analysis) ppm avcl day, ppm avcl Treated Water Used#1 0 296.96 0.00 20.0 0.00 0.00 5.5 225.11 71.85 20.0 2.15 64.50 1.1 4.924 147.24 149.72 20.0 3.69 110.80 1.9 1.9 48 64.07 232.89 20.0 4.79144.00 2.5 1.3 72 28.80 268.16 20.0 4.89 147.00 2.6 0.9 #2 0 280.52 0.0020.0 0.00 0.00 5.5 260.03 20.49 20.0 0.88 26.50 0.5 2.0 24 241.93 38.5920.0 1.48 44.33 0.8 0.8 48 102.67 177.85 20.0 1.69 50.70 0.9 0.4 72 0.00280.52 20.0 2.06 61.75 1.1 0.4 #3 0 298.76 0.00 20.0 0.00 0.00 5.5304.98 0.00 20.0 0.64 19.10 0.3 1.5 24 288.78 9.98 20.0 1.20 35.98 0.60.6 48 176.08 122.68 20.0 1.77 53.20 0.9 0.5 72 69.00 229.76 20.0 2.4874.40 1.3 0.4 #4 0 278.74 0.00 20.0 0.00 0.00 5.5 279.47 0.00 20.0 0.721.00 0.4 1.6 24 249.58 29.16 20.0 1.28 38.37 0.7 0.7 48 130.63 148.1120.0 2.00 58.89 1.1 0.5 72 62.00 216.74 20.0 2.37 71.00 1.2 0.4

The average dissolving rate of each tablet is shown below:

Formulation Average Dissolving Rate 1 119 2 74 3 49 4 58

While the invention has been described above with reference to specificembodiments thereof, it is apparent that many changes, modifications,and variations can be made without departing from the inventive conceptdisclosed herein. Accordingly, it is intended to embrace all suchchanges, modifications and variations that fall within the spirit andbroad scope of the appended claims. All patent applications, patents andother publications cited herein are incorporated by reference in theirentirety.

1. A non-Division 5.1 Oxidizer tablet consisting essentially of a blendof hydrated calcium hypochlorite with magnesium sulfate heptahydrate,wherein the blend contains at least about 17% by weight of water basedon the total weight of the blend and the average dissolving rate of thetablet is less than 150 grams per day.
 2. The tablet of claim 1 whereinthe composition contains at least 25% by weight of magnesium sulfateheptahydrate and less than about 75% by weight of hydrated calciumhypochlorite.
 3. The tablet of claim 1 wherein the composition containsabout 25% to about 40% by weight of magnesium sulfate heptahydrate andabout 60% to about 75% of hydrated calcium hypochlorite.
 4. The tabletof claim 1 wherein the amount of water in the composition is from about18% to about 24% by weight of the composition.
 5. The tablet of claim 1wherein the avenge dissolving rate is less than about 100 grams per day.6. A non-Division 5.1 Oxidizer tablet consisting of a blend of hydratedcalcium hypochlorite with magnesium sulfate heptahydrate, wherein theblend contains at least 17% by weight of water based on the total weightof the blend and the average dissolving rate of the blend is less than150 grams per day.
 7. The tablet of claim 6 wherein the compositioncontains at least 25% by weight of magnesium sulfate heptahydrate andless than about 75% by weight of hydrated calcium hypochlorite.
 8. Thetablet of claim 7 wherein the composition contains about 25% to about40% by weight of magnesium sulfate heptahydrate and about 60% to about75% of hydrated calcium hypochlorite.
 9. The tablet of claim 8 whereinthe amount of water in the composition is about 18% to about 24% byweight of the composition.
 10. The tablet of claim 9 wherein the averagedissolving rate is less than 100 grams per day.